It has been demonstrated in our earlier patent application, Ser. No. 678,061, that permethrin incorporated into a fire retardant and water resistant coating on the inside of a tent provides protection against insects for as long as six months. The plasticizer in the coating provides the permethrin mobility to the coated fabric surface in a controlled release manner.
Since permethrin is prone to decomposition into an inactive non-insecticidal product in the presence of oxygen and ultraviolet light, it is important to minimize migration of the permethrin to the exterior surface of the tent or other fabric. The fabric substrate, itself, is recognized in our application Ser. No. 678,061 as functioning as a barrier to the migration of the permethrin from the coating on the inside of the fabric to the outside of the fabric, where it is exposed to oxygen and ultraviolet light.
As explained in our earlier application, Ser. No. 678,061, permethrin is a synthetic pyrethroid which exhibits repellent as well as knockdown and kill activity against insects. Pyrethroids, including both the naturally occurring compounds and their synthetically prepared analogs effectively control a variety of pests, such as houseflies, mosquitoes, cockroaches, etc.
They are not harmful to plants, food, animals and humans, and leave no harmful residues. Permethrin is environmentally safe and has been found to be compatible with coating compositions containing water repellent chemicals and flame retardant chemicals, used for tent fabric, without adversely affecting the desired properties of the coated fabric.
Despite these highly favorable characteristics, permethrin has had only limited general utility because of its relatively short-lived insecticidal activity. This is due to its decomposition into an inactive, non-insecticidal product in the presence of oxygen and ultraviolet light. The speed of this decomposition is dependent upon the environment in which the permethrin is placed, but typically takes place in from several hours to several days or weeks. The instability of permethrin severely limits its usefulness as an insecticide.
Prior attempts to stabilize pyrethroids against degradation have included encapsulation and the addition of antioxidants and photostable ultraviolet light absorbent compounds to solutions of pyrethroids. Encapsulation has not been effective because the pyrethroids degrade almost as quickly inside the capsules as they do unencapsulated. Only moderate success in reducing degradation has been obtained by the addition of antioxidants and photostable ultraviolet light absorbent compounds to solutions of pyrethroids. Their moderate success is largely off-set by unsightly residues which are hard to remove.
Various techniques have been suggested for providing sustained release of a pyrethroid as an insect control agent. For example, U.S. Pat. No. 4,056,610 to Barber discloses a microcapsule insecticide composition in which a pyrethroid permeates a porous shell wall and maintains an effective level of the pyrethroid upon the outer surface of the shell wall to control insects for up to four days (then considered an extended length of time within the art). Control is achieved by killing insects which contact the pyrethroid released through the capsule wall.
U.S. Pat. No. 4,765,982 to Ronning discloses an insect control device comprising a plurality of rough surfaced cellulosic fibers wherein there is self-adhered to the surface of the fibers a liquid insecticide composition microencapsulated in a capsule whose shell is permeable to the liquid insecticide. The micro-encapsulated insect control agents disclosed in U.S. Pat. No. 4,956,610 to Barber are named as the preferred insecticide for use in Ronning's invention.
Ronning's insecticide-treated-rough-surfaced cellulosic fibers are formed into webs, tapes, sheets, pads, and various other relatively flat shapes suitable for use in particular locations, such as a ribbon-like tape for placement along the base of a building or door.
Ronning teaches that smooth-surfaced fibers do not act as good sites for adhesion of microencapsulated insect control agents. Ronning's rough surfaced cellulosic fibers treated with an insecticide are not suitable for a tent fabric. The texture of the rough surfaced fibers is not satisfactory and they are neither water repellent or flame retardant.